Bearing surfaces of joints may become worn or damaged by arthritis over time. Where this occurs, it is common to replace the damaged surface with an artificial surface in the form of a prosthetic.
In a knee replacement, the bearing surfaces are replaced by a prosthetic which comprises a femoral implant and a tibial implant (tibial tray), which interface through a bearing disposed between the two implants.
A unicompartmental or partial knee replacement may be carried out where only one of the medial or lateral compartments is damaged. This helps to conserve undamaged bone and restores more natural movement. Also, due to the small size of the prosthetic, the surgery may be less invasive than a total knee replacement.
Following resection of the joint surfaces to remove the damaged bone, the prosthetic implants are secured to the resected bone. For the tibial implant, a slot is cut into the tibial plateau to receive a keel which protrudes from a bottom surface of the tibial implant.
The keel of the tibial implant may be secured in the slot by a self curing polymer compound known as bone cement. However, the bone cement may degrade over time and crack. As an alternative, the slot may be sized so that the keel and slot have an interference fit. In this case, no cement is require and the implant is secured solely by the interference fit. This method of fixation is commonly known as ‘cementless’.
Where a cementless implant is used, it is necessary to force the keel into the slot. Due to the size of the operative wound, particularly in a unicompartmental or partial knee replacement, it is difficult for the surgeon to provide the necessary force in order to force the keel into the slot. To aid the surgeon, a tibial impactor may be used. A tibial impactor has an impaction member which is inserted into the operative wound and a extension arm which is connected to the impaction member but extends out of the operative wound. The extension arm transfers a force applied to it, for example by a hammer, to the impaction member located within the operative wound such that the impaction member contacts the tibial implant and forces the keel into the slot in the tibial plateau. The extension arm may extend above the femur and have a portion which extends parallel with the impaction member.
Since the impaction member enters the operative wound it is essential that it is satisfactorily sterilised and free from germs in order to prevent infection of the wound. The present invention therefore seeks to provide a surgical impactor which may be easily sterilised.